A movable contact unit formed by bonding a movable contact shaped like a dome onto flexible insulating film is widely used in switches of operating panels of various electronic devices. FIG. 14 shows a sectional view of a conventional movable contact unit. The unit shown in FIG. 14 is enlarged in a thickness direction in order to show the structure more understandably. Adhesive layer 2 is prepared beneath flexible insulating film 1, and plural movable contacts 3 shaped like domes and made of conductive thin metal plates are bonded onto adhesive layer 2, so that plural movable contact units 30 are formed.
A placement of the plural movable contact units is determined depending on each one of the switches of an operating panel. FIG. 15 shows a perspective exploded view of a movable contact unit to be used in a cellular phone. Plural movable contacts 3 or 4 forming plural movable contact units are placed as illustrated.
FIG. 16 shows a sectional view illustrating a conventional switch of an operating panel. A movable contact unit having movable contacts 3 is bonded onto circuit board 7 having fixed contact 6 (contacts 6A, 6B) via adhesive layer 2. A center section of movable contact 3 opposes fixed contact 6A via a space, and a circumference of movable contact 3 is brought into contact with fixed contact 6B. A contact pair including a movable contact 3 and a fixed contact 6 forms an individual switch of the operating panel. Operating button 8 movable up and down is provided on each one of the movable contact units.
When depressing force applied to button 8 exceeds repulsive force of domed movable contact 3, contact 3 bows downward moderately as shown in FIG. 17, then the center section of contact 3 comes into contact with fixed contact 6A, so that fixed contacts 6A and 6B on circuit board 7 are electrically connected to each other via movable contact 3. Removing the depressing force applied to button 8 prompts resilient restoring force of contact 3 to restore button 8 and contact 3 to the original position shown in FIG. 16, so that the electrical connection between fixed contacts 6A and 6B on board 7 is disconnected.
In the movable contact units used in a cellular phone and shown in FIG. 15, the unit having movable contact 4 placed at the center of contacts 5 placed crosswise is used for an “enter” operation. Japanese Patent Application Non-Examined Publication No. 2002-216582 discloses that movable contact 4 has repulsive force greater than movable contacts 3 around contact 4 to prevent a careless “enter” operation. In this case, it is difficult for movable contact 4 to obtain satisfactory durability while contact 4 gets greater repulsive force than movable contacts 3 and maintains the same dimensions as contacts 3.